In general, ink ribbon cassettes having thermal transfer ink ribbons are widely used in printing equipment such as a printer or the like. A thermal head of a printer abuts against an ink ribbon to thermally transfer the dye and pigment of the ink ribbon to a sheet superposed on the ink ribbon for printing. During printing, such a thermal transfer ink ribbon is supplied from an ink ribbon reel-out shaft of a reel-out shaft holder of the ink ribbon cassette and reeled in around an ink ribbon reel-in shaft of a reel-in shaft holder of the ink ribbon cassette.
More specifically, with reference to FIG. 9, a conventional ink ribbon cassette 30 is provided with a shaft container 41. This shaft container 41 includes a reel-out shaft holder 37, a reel-in shaft holder 39 and a pair of lateral bodies 33. The reel-out shaft holder 37 has a reel-out shaft bearing 31 that journals an ink ribbon reel-out shaft 35 winding an ink ribbon 34 therearound. The reel-in shaft holder 39 has a reel-in shaft bearing 32 that journals an ink ribbon reel-in shaft 36 securing one end of the ink ribbon 34. The lateral bodies 33 connect the reel-out shaft holder 37 with the reel-in shaft holder 39. A reel-out shaft holder cover 38 and a reel-in shaft holder cover 40 are each provided separately from the shaft container 41. The reel-out shaft holder cover 38 is adapted to cover the reel-out shaft holder 37 of the shaft container 41. The reel-in shaft holder cover 40 is adapted to cover the reel-in shaft holder 39 of the shaft container 41.
In order to manufacture the ink ribbon cassette 30, the shaft container 41, the reel-out shaft holder cover 38 and the reel-in shaft holder cover 40 are molded separately from one another by an injection die. Thereafter, the reel-out shaft holder cover 38 and the reel-in shaft holder cover 40 are manually assembled to the shaft container 41.
In this case, the reel-out shaft holder cover 38 and the reel-in shaft holder cover 40 are provided with fitting members 38a and 40a, respectively, as shown in FIG. 9. When the reel-out shaft holder cover 38 is assembled to the shaft container 41, the fitting members 38a of the reel-out shaft holder cover 38 are internally snap-engaged with the reel-out shaft holder 37 of the shaft container 41. Similarly, when the reel-in shaft holder cover 40 is assembled to the shaft container 41, the fitting members 40a of the reel-in shaft holder cover 40 are snap-engaged with fitting apertures in the reel-in shaft holder 39 of the shaft container 41.
In this case, as shown in FIG. 9, the fitting members 38a of the reel-out shaft holder cover 38 are provided inside the reel-out shaft holder cover 38 and similarly also the fitting members 40a of the reel-in shaft holder cover 40 are provided inside the reel-in shaft holder cover 40. Therefore, when the reel-out shaft holder cover 38 and the reel-in shaft holder cover 40 are assembled to the shaft container 41, the shaft container 41 has no portion projecting outwardly from a front surface 37a of the reel-out shaft holder 37 and from a front surface 39a of the reel-in shaft holder 39.
After the reel-out shaft holder cover, the reel-in shaft holder cover (hereinafter, these are also simply called the covers) and the shaft container have been assembled with each other, a drop test is generally performed to confirm the strength of the assembled ink ribbon cassette by dropping it. This drop test requires the covers and the shaft container not to be disengaged from each other when the ink ribbon cassette is dropped from a certain height.
In order to pass the drop test, a preliminary drop test is performed using an ink ribbon cassette made by assembling the reel-out shaft holder cover, the reel-in shaft holder cover and the shaft container with each other. The respective shapes of injecting dies used to mold the covers and shaft container, especially, the respective shapes of the fitting members and fitting apertures (hereinafter, these are collectively called the fitting portions) are adjusted based on the results of the preliminary drop test. Such a drop test is repeated one or more times and the respective shapes of the fitting portions are adjusted for each drop test.
On the other hand, in the injection die for the covers of the ink ribbon cassette, one die is provided with cavities corresponding to a plurality of covers. Accordingly, the plurality of covers can be molded by injecting a synthetic resin into one injection die.
For example, assume that one injection die is provided with cavities A1 and A2 of the cover A, and another injection die is provided with a (single) cavity B1 of a shaft container B. In this case, it is necessary to adjust the injection die so that both combinations, i.e., a combination of the cover A1 and the shaft container B1 and a combination of the cover A2 and the shaft container B1, may pass the drop test.
In addition, there may be covers (e.g., C1 and C2) different from these covers in some cases. In such cases, it is time consuming to adjust an injection die for the fitting states of the fitting portions in all the combinations of the covers with the shaft container in the ink ribbon cassette. For this reason, it is effective that the covers and the shaft container are formed integrally with each other and molded by a single injection die, and a fitting state is adjusted only for the injection die.
Patent Document 1: JP-A-4-50259
Patent Document 2: JP-A-9-136464
Patent Document 3: JP-A-10-193760
Patent Document 4: JP-A-2005-47222
In recent years, along with downsizing of printers, ink ribbon cassettes attached to the printers have been downsized. If the ink ribbon cassette has a portion projecting from the surface thereof, such a portion may be likely to become an obstacle when the ink ribbon cassette is internally attached to the printer at a predetermined position. Thus, it is preferred that such a portion projecting outwardly from the ink ribbon cassette not be present.